From my point of view, you can really do 2 things to make a relationship fun again.
Challenge/Mystery-Challenge is necessary in a relationship. But its not what many ppl perceiveiy to actually be. It's not about playing games and "acting" to not see her/care about her. It's actually about being active pursuing your passions and the things in life that mean something to you. If you're ambitious and you're both interested and interesting, you'll just come across as a natural challenge. Which is what everyone should strive for btw. I'm not there yet. I ean sometimes, I catch myself pretending I'm busy when I'm not. In the end, just keep yourself busy, so you wont have to worry about lying.
Just finding fun things to do together-I like this method much more than the incorrect perception of what ppl here see as challenge (waiting to phone a few days in order to "up" her IL), keeping the phone call really short because you're acting lie your busy when really u have nothign to do)..The point is, instead of focusing solely on YOU, focus a bit on HER. Bring her to do fun stuff. Have amazing, varying sex, take her on action dates. Go on trips with her etc etc.
Another way to interpret challenge and mystery in my opinion anyways is not only to be "unavailabe" to talk or see eachother. That was the 1st type of challeneg and mystery I mentioned. Of course you can be that guy by actually having a life, like I also mentioned before.
But another helpful way of achieving mystery and challenege is not through the frequency in which you spend time togther, but ALSO by becoming a more interesting person altogether. You can achove this through self improvement and by LIVING LIFE. What you'll find is that the more you do this, the more layers you will have to your "man"hood and overall disposition. You become a challenege when you're not quickly figured out. This is not gained by faking being busy, but also by encouraging and manifesting your many "facets" into your personhood. I dont know if you understand what I'm saying. If you don't, drop me a line.
IMO, being amazing with women requires you to master the internal as well as the external.
It's the combination of these two things that makes you irresistible. By internal, I mean you have to learn to respect yourself and have confidence. This is achieved by living your life the way you want it and improving yourself every single day. It's funny that so many ppl have the misperception that having yourself mastered and "mastering" girls are in completely different realms. The point is, the better you become, the more you appreciate yourself and life in general..getting woman's attention because of this direct consequnce should be seen as icing on the cake..
Anyways, I'm rambling. In short, by focusing on yourself, not only are you making things more interesting for the women you encounter in everyday life, but you also become a better, happier person.
